The present invention pertains to the texturing of magnetic disks. More particularly this invention pertains to using a near infrared wavelength laser to create bumps on a nonmetallic substrate based magnetic disk.
A direct access storage device uses magnetic disks to store electronic data. The disks are rotated on a central axis in combination with magnetic heads for reading and writing magnetic signals.
A xe2x80x9ccontact start/stopxe2x80x9d (CSS) system uses a magnetic head which is in contact with the magnetic disk surface only when the disk is stationary. When the disk starts to rotate the magnetic head slides off the surface eventually flying fully lifted from the disk surface.
A smooth recording surface is preferred to permit the magnetic head to ride as close as possible to the disk surface. In order to avoid stiction, which occurs during the start process in a CSS system, a textured region of the rotating disk surface is used for the contact area with the magnetic head. The surface texture in a contact start/stop region reduces the contact stiction and friction. The magnetic head is moved to the contact region at the appropriate times by the drive controller.
It is known in the art to use a laser to create bumps on the surface of the disk to produce a textured region as a contact area in a CSS disk drive system. Laser zone texturing (LZT) processes are widely used in the hard disk drive industry to allow precise control of the roughness of the hard disk contact area. In laser zone texturing, an annular area typically 2-3 mm wide of the disk surface is roughened by a laser. The laser produces micro-sized bumps to provide a take off and landing zone for the flying head during the contact start/stop operation. Usually, the laser texturing process is applied to a nonmagnetic substrate prior to conventionally employed processes for producing the magnetic recording disks.
Traditionally, a magnetic disk is manufactured by initially starting with an aluminum magnesium (AlMg) substrate which is then plated with nickel phosphorus (NiP). The texturing is then performed on the plated NiP layer. On top of the NiP plated AlMg substrate, a magnetic layer is sputter deposited.
In particular, because of their performance characteristics, it is desirable to use a tightly focused laser beam, with TEM00 spatial mode and Gaussian intensity distribution profile, from diode pumped neodymium-doped yttrium-lithium-fluoride (Nd:YLF) or a neodymium-doped yttrium-vanadate (Nd:YVO4) solid state laser to create the bumps on a disk surface. The Nd:YVO4 laser is also referred to as an Nd:Vanadate laser or a Vanadate laser. These lasers are in the near infrared (near-IR) family of lasers. The near-IR wavelength lasers provide sufficient absorption and coupling of laser energy into the smooth amorphous NiP material that had been deposited onto the AlMg substrate.
An example of a laser texturing tool is provided in commonly owned U.S. Pat. No. 6,013,336, Baumgart et al, xe2x80x9cProcedure Employing a Diode Pumped Laser for Controllably Texturing a Disk Surfacexe2x80x9d. Other laser texturing tools are well known to those skilled in the art.
In the last few years the use of alternative nonmetallic substrates such as glass or glass-ceramic substrates has become widely accepted in the industry due to the superior mechanical advantages of glass and glass-ceramic material. A glass based substrate provides a smoother surface for the magnetic layer. The smoother the recording surface, the closer the proximity of the head to the disk. This allows more consistent and predictable behavior of the air bearing support for the head which enables a higher recording density.
However, since glass materials are optically transparent in the near IR wavelength range, the vanadate laser based texturing tools cannot be used for the laser zone texturing process on the raw glass substrate.
As an alternative laser texturing process, a CO2 laser based system is known in the industry to be used for zone texturing raw glass substrates. This is because the glass substrate material is sufficiently absorbent at wavelengths produced by CO2 lasers. The textured glass substrate can then be processed to the finished magnetic disk by depositing at least one underlayer, then a magnetic layer and then a protective overcoat (commonly a carbon or carbon-based layer). Examples of a laser texturing tool for glass substrates is found in commonly owned U.S. Pat. No. 6,107,599, Baumgart et al, xe2x80x9cMethod and Tool for Laser Texturing of Glass Substratesxe2x80x9d.
However, the bump formation mechanism as well as the bump shape for the above processes are different. Bump formation on a NiP-plated AlMg disks is governed by rapid melting and resolidification process of the heated spot on the substrate surface, and the final bump shape depends on thermocapillary and chemicapillary effects created by the laser pulse. While the bump formation on a glass disks (using CO2 laser) is due to laser absorption in the glass and the consequent thermal expansion of the heated area.
While the CO2 laser can be used to texture raw glass substrates, there are limitations in the ability of CO2 laser texturing tools to optimally texture disks. Therefore, it is desirable to provide a method for texturing the glass based substrate disks using the Nd:Vanadate laser because Nd:Vanadate lasers provides greater flexibility in the process of producing a textured zone.
Furthermore, the Nd:Vanadate laser texturing systems are currently widely used in the manufacturing texturing process of NiP-plated AlMg substrates. It is more economical to be able to use the more readily available laser systems for the glass substrate disks.
An approach to providing zone texturing of a glass substrate has been demonstrated in U.S. Pat. No. 5,980,997. In this approach, a smooth metallic layer is first deposited on a glass substrate, and the metallic layer is then textured by a laser beam. The metallic layer is preferably impact resistant, hard and has a high-melting temperature greater than 1000 degrees centigrade. Since such a deposited metallic layer (i.e., texture layer) absorbs laser energy at near-IR wavelengths, a Vanadate laser based texturing tool can be used to produce a textured zone on the glass substrate deposited with a texture layer. The textured glass substrate then undergoes the conventional processes for the manufacturing of a magnetic disk. A disadvantage of this approach is that an extra step is added to the manufacturing process of depositing a texture layer before the laser texturing process is completed. Such a step obviously adds to the manufacturing costs of a magnetic disk production. Therefore, there is a need for a laser texturing process for glass-substrate magnetic disks which does not add to any of the production costs and allows for greater flexibility in the use of the Vanadate-laser-based texturing tool.
It is also desirable to provide a process for marking a disk, including alphanumeric writing, on a sputtered or finished disk. Disk marking can be used to distinguish a good and a defective side of a single sided finished disk by producing a textured ring or other arbitrary pattern on the defective side of the finished glass disk. Such a marked finished glass disk can be used in a load/unload drive and not necessarily in a contact start/stop drive. Implementation of such marking process in manufacturing can extend applicability of the existing texturing systems to disk marking processes.
The marking of a disk can also be useful for identifying a disk. When a disk is in use, installed in a computer system, it is helpful to be able to determine when and where the disk was manufactured. Marking a disk with this information enhances quality assurance processes.
It is also desirable to use textured glass substrate disks to determine the glide height of a magnetic head over a magnetic disk. It is currently known in the industry to use textured disks to test whether a magnetic head flying over a disk touches the disk surface which causes problems.
During reading and recording operations, the head is positioned as close to the disk surface as possible. There are topological asperities, typically, only a few microns (or smaller) in diameter and height range from about a few micro-inches to sub-micro inches, formed on the surface of a disk which make it necessary to limit the proximity of the head to the disk surface. Conventional disk drives are manufactured with precise specifications including maximum glide height for a magnetic head above the data zone. In recognition of the inevitable topographical asperities, conventional practice comprises testing each magnetic disk to determine if the maximum glide height requirement is met. Such testing typically comprises the use of a device known as a glide tester.
Conventional glide testers typically use a reference disk containing a single (or multiple) protusions formed by photolythographic techniques, or single (or multiple) laser-textured bump(s) on AlMg substrates, or raw glass substrates, having a defined height. The referenced disk is rotated and a magnetic head is lowered until the magnetic head contacts the bump at which point an electrical signal is generated indicating the glide height. Of particular significance is the need for the bumps on the reference disk to accurately simulate asperities inevitably present on the surface of a magnetic disk. There exists a need for an efficient and cost-effective method to produce such a reference disk.
There is also a need to better control the shape and orientation of laser produced bumps to provide a more controllable contact start/stop zone wherein stiction is reduced without compromising durability. It is also desirable to control and adjust the bump shape for a glide tester reference disk to optimize electrical signal generation during the process of glide height calibration, and to overcome signal generation issues associated with CO2 laser produced bumps on raw glass substrates. More particularly, it is desirable to efficiently produce bumps with elongated shapes to achieve these goals.
One or more of the foregoing problems are solved and one or more of the foregoing needs are met by the present invention.
A magnetic disk is provided which comprises a glass or glass/ceramic substrate, one or more under layers, a magnetic layer applied over the substrate, and a carbon layer applied over the magnetic layer. A plurality of bumps are formed on the magnetic disk by applying a laser beam to the surface of the carbon layer.
In a further embodiment of the present invention a method is provided for preparing a magnetic disk comprising first applying one or more under layer(s) and a magnetic layer to a glass or glass ceramic substrate. A carbon overcoat layer is then applied over the magnetic layer. A plurality of bumps are incorporated onto the surface of the disk by applying a laser to the surface of the carbon layer. In a further embodiment a lubricant is applied over the carbon overcoat layer.
In a further embodiment of the present invention the bump formation process can be conducted after applying the lubricant layer on the magnetically sputtered disk.
In a further embodiment, a plurality of bumps formed in a concentric circle using the laser provides a contact start/stop zone for the magnetic disk.
In a further embodiment, a single or a plurality of bumps provide a means for calibrating glide height of a transducer head flying over the magnetic disk.
In a further embodiment, a plurality of bumps provide a means for marking the magnetic disk.
In a further embodiment, a cylindrical lens system is used to form elliptical or elongated bumps on the surface of the finished glass substrate magnetic disk.